The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Alluvial Fan, Kenai Peninsula, Alaska

Pictured above is an alluvial fan at the base of a seasonalwaterfall on the Kenai Peninsula in south-central Alaska. Alluvial fans are caused by rapid deposition of the suspended load of a stream when its gradient shallows to the point where it can no longer keep the material in suspension. The material deposits in accordance with Stoke’s Law, which states that particles drop out of suspension at a rate that's related to their diameter. Material is therefore sorted, with coarser grained sediments at the apex of the fan, closer to the source, and finer materials down-slope near the base. Note that growth that is more luxuriant occurs on the finer material. Photo taken on August 18, 2008.